Test apparatus for flight actuator check device

ABSTRACT

A test apparatus is provided for testing a sensorless check device of an actuator. The sensorless check device is arranged to be used by mechanically moving a check device pin from a resting position to an actuation position and then releasing the check device pin to allow it to return to a resting position urged by an elastic return mechanism. The test apparatus comprises: a piston for contact with an actuator surface associated with the check device pin; a piston spring for urging the piston toward the actuator surface, wherein the piston spring is softer than the elastic return mechanism of the check device; and an adjustment and testing mechanism.

FOREIGN PRIORITY

This application claims priority to European Patent Application No.17305589.8 filed May 19, 2017, the entire contents of which isincorporated herein by reference.

TECHNICAL FIELD

The invention relates to a test apparatus for testing the operation of acheck device for a flight actuator, such as a test device for a primaryload path failure detection device. A related method for testing theoperation of the check device is also described.

BACKGROUND

It is well known for flight actuators to include two mechanical loadpaths, one primary and the other secondary, with the latter intended totake up the load when the primary path has failed. In a typical priorart device, as shown in FIG. 1, when operating on the primary load paththe loads are transmitted through a hollow ball or roller screw. Thehollow screw houses a safety rod, also called a failsafe bar or tie bar,which is connected to the screw with a small amount of play. Duringnormal operation of the screw, when the primary load path is workingcorrectly, the secondary load path formed by this tie bar carries noload since there is no contact due to the small amount of play. However,in the event of a failure of the screw in the primary load path then thetie bar performs its failsafe function and ensures continuity of thetransmission of loads by the actuator.

With reference to FIG. 1 a typical known flight control actuator of thetrimmable horizontal stabiliser actuator (THSA) type includes a primaryload path with a hollow screw 2 connected at its upper end to theaircraft via a Cardan joint system 4 joining with first aircraftstructural elements 5. The primary load path further includes a nutassembly (not shown) mounted on the screw 2, and the nut assembly isconnected to the stabiliser of the aircraft, this connection beingachieved for example by another Cardan joint system.

The secondary load path is provided by means of a tie bar 3 which iswithin the screw 2. The tie bar 3 is terminated at its upper end by amale portion, in this case taking the form of a spherical head 7, whichis mounted within a recess on a fastening piece 8. The fastening piece 8is connected to the structure of the aircraft via second aircraftstructural elements 9. The known system may also include some means forpreventing motion of the nut assembly relative to the screw 2 and/or forfixing the stabiliser in place when the primary load path fails. Thus,the lower attachment, of which the nut assembly is a part, could alsoinclude secondary load path elements used when the primary load pathfails.

A flight actuator with the basic features discussed above can be foundin the prior art, for example in U.S. Pat. No. 8,702,034 and in US2013/105263. It is beneficial to provide a detection device fordetecting the failure of the primary load path in a reliable andeffective manner. In addition, it is desirable to be able to check thatthe detection device is operating correctly. In the prior art, US2013/105263 discloses a device for detecting the breakage of a primarypath in a flight control actuator, said actuator having a primary pathcomprising a rotary hollow screw and a secondary path comprising asafety rod that reacts the load passing through the screw. The device ofUS 2013/105263 comprises a position sensor, connected to the screw, tomeasure information representative of the angular position thereof, anda disconnection system able to disconnect the screw position sensor inthe event of relative movement of the rod with respect to the screw ifthere is a break in the primary path. Thus, when the primary path failsthe disconnection system disconnects the screw position sensor and it ispossible for the pilot to be alerted of a primary path failure.Advantageously this prior art system does not need the addition of newsensors to detect the primary path failure, since the position sensor isgenerally already present for the purpose of determining the position ofthe screw to thereby determine the actuator position.

EP3081481 discloses a so called ‘sensorless’ check device for theprimary load path failure detection device, wherein a mechanical linkagesimulates disconnection of the position sensor of the detection deviceby permitting relative movement of at least first and second mechanicalparts of the actuator that are unable to move relative to one another innormal use without failure of the primary load path. The first andsecond mechanical parts include a mechanical part with movement detectedby the position sensor of the primary load path failure detectiondevice, which in the example of EP3081481 involves disengaging rotationof the position feedback gear using a sprung fuse piston.

The primary load path failure detection device and the sensorless checkdevice proposed in EP3081481 are shown in FIGS. 2 to 9, which aredescribed in more detail below. With a check device of this type theprimary load path failure detection device can be triggered by means ofthe sensorless check device, which operates in a purely mechanicalmanner. By the use of a mechanical linkage it is possible to test boththe mechanical elements and also the electrical elements of the primaryload path failure detection device, since the system uses a mechanicalmovement of the relevant parts and this can be checked by means ofelectrical signals from the position sensor. No additional sensors arerequired since the check device makes use of the same sensor as theprimary load path failure detection device. Such a sensorless checkdevice provides a highly reliable way to ensure correct operation of theprimary load path failure detection device. There is however a need toensure that the sensorless check device is itself in good working order.

SUMMARY

Viewed from a first aspect, the invention provides a test apparatus fortesting a sensorless check device of an actuator, wherein the sensorlesscheck device is arranged to be used by mechanically moving a checkdevice pin from a resting position to an actuation position and thenreleasing the check device pin to allow it to return to a restingposition urged by an elastic return mechanism, the test apparatuscomprising: a piston for contact with an actuator surface associatedwith the check device pin; a piston spring for urging the piston towardthe actuator surface, wherein the piston spring is softer than theelastic return mechanism of the check device; and an adjustment andtesting mechanism; wherein the adjustment and testing mechanism isarranged to: compress the piston spring and apply a load via the pistonto the actuator surface to move the actuator surface so that theposition of the piston at the start of the movement of the actuatorsurface can be recorded in order to establish a reference position,depress the check device pin via the piston and actuator surface tosimulate use of the check device, allow the check device pin to returntoward the reference position being urged by its elastic returnmechanism, and indicate when the check device pin reaches a finalposition after being released by indicating when the actuator surface isno longer applying a force to the piston, such that the final positionof the check device pin can be compared to the reference position.

This apparatus may advantageously allow for a fully mechanical testingof the check device based on firstly ensuring that the device movesthrough its required range of travel, and secondly ensuring that thedevice returns to its starting position after use, or at least that anydifference in position is within predetermined tolerances. Thus, thetesting device can ensure that there is no jamming or sticking of parts,and that the movement of the device is within design limits.

The elastic return mechanism of the check device may consist of one ormore springs or similar resilient devices arranged to urge the checkdevice back to its resting position. For example, the check device pinmay be connected to a spring that acts to push the check device pin backto its resting position after actuation to check the actuator. The checkdevice pin is moved by a force applied on the actuation surface and insome cases the actuation surface may be on a separate part that ismechanically coupled to the check device pin, such as an externalactuator. The external actuator may have a spring return or similarresilient device that contributes to the elastic return mechanism of thecheck device pin.

The piston spring of the testing apparatus is softer than the elasticreturn mechanism such that the piston spring will compress before thereis movement of the check device pin against the resistance of theelastic return mechanism. The piston spring ensures that the piston willremain in contact with the actuator surface when the actuator surfacestops moving and hence that the piston will move relative to other partsof the testing apparatus when the actuator surface is no longer applyinga force to the piston, that is to say, when the elastic return mechanismhas reached the end of its travel. Thus, the piston spring may be aresilient device with a spring stiffness that is less than the springstiffness of the elastic return mechanism of the check device with whichthe testing apparatus will be used. The stiffness of the piston springmay hence be selected based on a known property of the check device. Toensure that there is no movement of the check device whilst the pistonspring is being compressed then the spring stiffness of the pistonspring may be less than a half of the spring stiffness of the elasticreturn mechanism, optionally less than a quarter thereof.

The testing apparatus may include a mounting part for attachment of thetesting apparatus to a casing that surrounds the check device. This maybe a casing of the check device, or a casing of a larger system thatincorporates the check device, such as a casing of a primary load pathfailure detection device comprising the check device or a casing of theactuator that is associated with the check device. The mounting part mayinclude a coupling mechanism for securely anchoring the testingapparatus to the casing. For example a screw fitting may be used. Inthat case the mounting device may be a mounting sleeve with a screwthread. Using a mounting part to securely attach the testing apparatusto the casing ensures that the position of the check device pin relativeto the testing apparatus is also a position of the check device pinrelative to the casing, which in turn ensures that any inconsistentmovement of a mechanical linkage associated with the check device pincan be reliably identified due to differences between the referenceposition and the final position.

The adjustment and testing mechanism may include an adjustment partarranged for movement relative to other parts of the testing apparatusin order to compress the piston spring and bear against the piston toallow a load to be applied to the actuator surface via the piston. Theadjustment and testing mechanism may include a testing part arranged formovement relative to other parts of the testing apparatus in order tomove the piston and to apply a load to the actuator surface via thepiston in order to move the check device pin against the resistance ofthe elastic return mechanism. The testing part may be arranged to movethe piston and push the actuator surface of the check device by adistance sufficient to bring the check device into operation. Forexample, in the case of a check device that operates by using amechanical linkage that simulates disconnection of a position sensor bypermitting relative movement of at least first and second mechanicalparts of the actuator then the testing part may be arranged to move theactuator surface by a distance sufficient to simulate the disconnectionof the position sensor. Thus, the degree of movement of the testing partin order to prompt movement of the actuator surface with a load appliedby the testing part may be set based on a known degree of movement ofthe check device.

The reference position and the final position may be determined based onthe relative location of the piston and another part of the testingapparatus. For example, the reference position and the final positionmay be determined based on the relative location of the piston and apart of the adjustment and testing mechanism. In one example, thereference position and the final position are determined by aligning thetesting part of the adjustment and testing mechanism with an alignmentmarking on the piston and then measuring a distance between the testingpart and the adjustment part of the adjustment and testing mechanism.This may be done by measuring between reference points on the adjustmentand testing mechanism, or alternatively the adjustment and testingmechanism may include a scale allowing a measurement to be read from theadjustment and testing mechanism.

The adjustment and testing mechanism may be attached to the mountingpart in order to allow for movement relative to the casing during use ofthe testing apparatus. In one example the adjustment part of theadjustment and testing mechanism is moveably attached to the mountingpart and the testing part of the adjustment and testing mechanism ismoveably attached to the adjustment part. The moveable attachment mayuse a screw thread, for example. The adjustment part may take the formof an adjustment nut with a thread for moveably attaching the adjustmentnut to the mounting part. The adjustment nut and the testing part mayeach comprise a screw thread for moveably attaching the testing part tothe adjustment nut, and in this case the testing part may take the formof a testing nut.

With the above arrangement the testing apparatus may comprise a mountingpart for coupling to the casing, an adjustment nut moveably attached tothe mounting sleeve and a testing nut moveably attached to theadjustment nut. The adjustment nut may be arranged to move relative tothe mounting part in order to compress the piston spring and bring thetesting nut into a mechanically coupled arrangement with the actuatorsurface via the piston. The testing nut may be arranged to move relativeto the adjustment nut in order to move the piston and thereby move theactuator surface in order to operate the check device. Where the testingnut uses a screw thread to connect to the adjustment nut then thetesting nut may be screwed and unscrewed in order to depress the checkdevice pin via the piston and actuator surface and to then allow thecheck device pin to return toward its start position under the influenceof the elastic return mechanism.

The testing apparatus may include a piston guide part for holding thepiston and guiding motion of the piston. The piston guide part may alsohave the function of holding the piston spring, such that the pistonspring can be compressed between the piston and the piston guide part.The piston guide part may take the form of an inner sleeve that islocated about the piston and that may fit closely with the piston inorder to guide a sliding motion of the piston within the inner sleeve.The piston guide part may be held within the mounting part and mayoptionally be moveably attached to the mounting part, for example with asliding arrangement. In this way the piston guide part may move relativeto and/or with the piston as well as moving relative to the mountingpart, and hence moving relative to the casing.

The piston guide part may include a shoulder for engaging with andpushing the piston. In this case, the adjustment and testing mechanismmay be arranged to come into contact with the piston guide part in orderto push the shoulder of the piston guide part into engagement with thepiston in order to move the piston and thereby move the check devicepin. Where the adjustment and testing mechanism includes an adjustmentpart and a testing part then the testing part may be brought intocontact with the piston guide part in order to push the shoulder of thepiston guide part into engagement with the piston. This may be done bymovement of the adjustment part to move the testing part relative to themounting part. The testing part may then be moved relative to theadjustment part in order to push the piston and depress the check devicepin as discussed above.

In one example the testing apparatus includes: a mounting sleeve with acoupling mechanism for securely anchoring the testing apparatus to thecasing; an inner sleeve that is held for sliding movement relative tothe mounting sleeve, wherein the inner sleeve holds and guides motion ofthe piston, holds the piston spring such that the piston spring can becompressed between the piston and the inner sleeve, and includes ashoulder for engaging with and pushing the piston; an adjustment nutmoveably attached to the mounting sleeve; and a testing nut moveablyattached to the adjustment nut; wherein movement of the adjustment nutwill bring the testing nut into contact with the inner sleeve to loadthe piston spring and bring the shoulder of the inner sleeve intoengagement with the piston; wherein subsequent movement of the testingnut will move the piston to thereby move the actuator surface in orderto allow for the check device pin to be depressed; and wherein thepiston is provided with an alignment marking for alignment with thetesting nut in order to determine the reference position and the finalposition.

In one example the testing apparatus is incorporated in a system forchecking a flight actuator, wherein the flight actuator comprises asensorless check device and wherein the system comprises the sensorlesscheck device and the testing apparatus. The sensorless check device maybe a check device for a flight actuator primary load path failuredetection device of the type that disconnects a position sensor from theprimary load path in the event of a primary load path failure, the checkdevice comprising: a mechanical linkage for simulating disconnection ofthe position sensor by permitting relative movement of at least firstand second mechanical parts of the actuator that are unable to moverelative to one another in normal use without failure of the primaryload path, wherein these first and second mechanical parts include afirst mechanical part with movement detected by the position sensor ofthe primary load path failure detection device.

The primary load path failure detection device may be of the type thatincludes the position sensor as a first position sensor for detectingthe position of the primary load path based on movement of the firstmechanical part, and also includes a second position sensor fordetecting the position of the primary load path based on movement of thesecond mechanical part. Advantageously the two position sensors and theassociated mechanical parts may be elements that are already present inthe flight actuator system, hence avoiding the need to introduceadditional mechanical or electrical parts for implementation of theprimary load path failure detection device. This also minimises theadditional parts required for the check device.

The primary load path failure detection device may be of the type thatincludes a releasable element normally coupled between the mechanicalparts and acting to inhibit relative movement thereof, and thisreleasable element may be used as a part of the check device. Thus, thecheck device may incorporate a releasable element of the primary loadpath failure detection device, this releasable element being coupledbetween the mechanical parts as noted above. The releasable element isadvantageously arranged to be disconnected upon failure of the primaryload path, wherein the disconnection of the releasable elementdisconnects the position sensor from the primary load path, optionallyby disconnection of the first mechanical part from the primary loadpath.

The releasable element may be a releasable pin element, for example apin that is in normal use coupled between elements of the primary loadpath and the secondary load path, and is released upon failure of theprimary load path. One possible form for this releasable pin element isa breakable pin (or fuse pin) arranged to be broken when load istransferred from the primary load path to the secondary load path. Asuitable breakable pin is disclosed, for example, in US 2013/105623. Inthis case the release of the pin takes the form of shearing of a part ofthe pin originally held by the secondary load path, and subsequentfreedom of the pin to rotate.

The position sensor, and optionally the second position sensor ifpresent, may be any suitable sensor type, for example a sensor fordetecting an angular position of a mechanical part, or a sensor fordetecting a linear motion, where the angular position or the linearmotion results from a change in position of a drive element of theprimary load path, which may for example be a screw.

In some example embodiments the mechanical parts are gears coupled to ascrew in a primary load path of the actuator. The gears may be arrangedsuch that in normal use they rotate together, and the mechanical linkageof the check device may be arranged such that, when actuated, it movesone of the gears relative to the other. Preferably the movement of thegear that is moved is detected by the position sensor. With thisarrangement it will be understood that it is easily possible to ensurethe correct operation of the primary load path failure detection devicesince when the mechanical linkage of the check device is actuated thenboth the mechanical functioning of the gears and the electricaloperation of the position sensor will be tested. The primary load pathfailure detection device should hence provide a signal indicatingfailure of the primary load path whenever the check device is actuated.The operator can ensure that the primary load path failure detectiondevice is operating correctly by means of the check device and withoutthe need for extensive testing procedures.

One possible form for the mechanical linkage is a connecting rod coupledbetween a releasable element of the check device (which may be areleasable element of the primary load path failure detection device asdiscussed above) and the first mechanical part, with the connecting rodarranged to move the first mechanical part relative to the secondmechanical part when the mechanical linkage is actuated. In an examplethe first mechanical part is a first gear, a first end of the connectingrod is mounted on a slider permitting movement of the rod along a radialdirection of the gear, and a second end of the connecting rod extendsinto a slot, the slot having a diagonal extent along both the radial andcircumferential directions of the gear. Thus, when the slider movesradially and the first end of the connecting rod therefore movesradially then the second end of the connecting rod is urged along theslot with both radial and circumferential movement resulting in arelative circumferential movement of the gear and the releasableelement, and hence simulating temporary disconnection of the gear.

The first end of the connecting rod may be connected to a slider at thereleasable element with the second end of the connecting rod extendinginto a slot formed on the gear. This arrangement enables simpleactuation of the mechanical linkage by pushing the slider and/or thereleasable element in the radial direction. In this case the slider maybe formed as a sleeve coupled to the releasable element, with thereleasable element moving with the sleeve and optionally the sleeve alsomoving relative to the releasable element. Alternatively, it would bepossible for the slider to be on the gear and the slot to be formed atthe releasable element. The connecting rod might be formed integrallywith the slider, or held in a bore on the slider.

The mechanical linkage of the check device may be arranged to beactuated from outside of the flight actuator, i.e. without the need toremove a casing or housing of the flight actuator. In some exampleembodiments the mechanical linkage is actuated by operation of a buttonor lever outside of the flight actuator casing, with the operation ofthe button or lever moving mechanical parts within the casing. The checkdevice may include a button arranged for linear movement and accessiblefrom outside of the flight actuator casing, with the linear movement ofthe button actuating the mechanical linkage, for example by providing alinear movement of a slider moving a connecting rod as described above.

The mechanical linkage may be provided with a spring return or otherresilient mechanism that opposes the forces applied to actuate themechanical linkage and returns the mechanical linkage to its at restposition after these forces are removed. Where a slider is present, asdescribed above, then there may be a spring return for urging the sliderto an at rest position where the first gear moves together with thesecond mechanical part. This ensures that during normal use the primaryload path failure detection device is not activated.

In one example the testing apparatus is incorporated in a system forchecking a flight actuator, wherein the flight actuator comprises aprimary load path failure detection device incorporating a sensorlesscheck device, which may be as described above, and wherein the systemincludes the flight actuator as well as a testing apparatus as describedabove. The primary load path failure detection device may have featuresas described above, and in particular may include a position sensorconnected to a screw of the actuator and being for measuring informationrelating to the position of the screw, along with a disconnection systemarranged to disconnect the position sensor from the screw in the eventof failure of the primary load path, for example as a result of relativedisplacement of the screw of the primary load path compared to a rod ofa secondary load path of the actuator.

The detection device may include a calculator arranged to receiveinformation from the position sensor, to receive information measured bya second position sensor that is independent of the disconnection systemand to compare the information from the two position sensors in order toindicate when there has been a failure of the primary load path.

In a further aspect the invention provides an attachment, for example alower attachment, for a flight actuator, the attachment including aprimary load path failure detection device as described above.

In another aspect the invention further provides a flight controlactuator including: a primary load path with a hollow screw; a secondaryload path having a rod passing through the screw, the secondary loadpath being arranged to take over the load exerted on the primary loadpath in the event of a break in the primary load path; and a primaryload path failure detection device including a check device as describedabove.

Viewed from a yet further aspect, the invention provides a method fortesting the operation of a sensorless check device for a primary loadpath failure detection device, wherein the sensorless check device hasan actuator surface associated with a check device pin and an elasticreturn mechanism for returning the actuator surface and the check devicepin to a start position after use, the method comprising: bringing apiston of a testing apparatus into contact with an actuator surfaceassociated with the check device pin, wherein a piston spring of thetesting apparatus urges the piston toward the actuator surface, andwherein the piston spring is softer than the elastic return mechanism ofthe check device; compressing the piston spring until a load can beapplied via the piston to the actuator surface to move the actuatorsurface; recording the position of the piston at the start of themovement of the actuator surface in order to establish a referenceposition; depressing the check device pin using the testing apparatus tosimulate use of the check device; releasing the check device pin andallowing it to return toward the reference position being urged by itselastic return mechanism; determining when the check device pin reachesa final position by determining when the actuator surface is no longerapplying a force to the piston; and comparing the final position of thecheck device pin to the reference position to ensure that the checkdevice pin returns to its original position.

This method ensures correct operation of the sensorless check device asdescribed above in relation to the testing apparatus of the firstaspect. The method may use the testing device of the first aspect. Thestep of comparing the final position of the check device pin to thereference position to ensure that the check device pin returns to itsoriginal position may include a visual check for alignment of thetesting apparatus against the check device pin, for example by checkingfor alignment of one or more marking(s) on at least one of the testingapparatus and the check device pin.

The method may include using a testing apparatus having any of thefeatures set forth above, optionally in conjunction with a sensorlesscheck device having any of the features set forth above. The sensorlesscheck device may be incorporated into a primary load path failuredetection device as discussed above, which may itself be a part of anattachment or of a flight actuator as discussed above. The method may becarried out during maintenance of an aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the invention will now be described byway of example only and with reference to the accompanying drawings inwhich:

FIG. 1 discloses a prior art flight actuator;

FIG. 2 is a schematic representation of a known detection device fordetecting primary load path failure in a flight control actuator;

FIG. 3 shows the detection device and actuator of FIG. 2 when theprimary load path has failed;

FIG. 4 is a schematic representation of a flight control actuatorsimilar to FIG. 2 with a detection device shown in greater detail;

FIG. 5 shows the detection device and actuator of FIG. 2 when theprimary load path has failed;

FIG. 6 illustrates parts of an actuator including a detection device fordetecting primary load path failure as well as a check device forensuring that the detection device is operating correctly;

FIG. 7 shows similar parts to FIG. 6 in cross-section;

FIG. 8 shows a feedback gear from actuator angular position measuringsystem and illustrates the link between the feedback gear and the checkdevice of FIGS. 6 and 7;

FIG. 9 is a cross-section of a similar check device to that of FIGS. 6and 7, when integrated into a casing having an external actuator for thecheck device; and

FIG. 10 shows a testing apparatus for testing operation of the checkdevice shown in FIGS. 6 to 9.

DETAILED DESCRIPTION

A primary load path failure detection device 13 for a flight controlactuator 12 is shown in FIG. 2. The flight control actuator 12 includesa primary load path 1 and a secondary load path 10. The actuator 12 is,for example, a THSA type actuator for controlling a variable horizontalcontrol surface of an aircraft (not shown). The primary and secondaryload paths 1, 10 include numerous elements, and only some of theseelements will be described. The basic structure of flight controlactuators comprising a primary and a secondary load path is known.

The actuator described here is of a mechanical type, using a rotatingscrew 2 for driving linear movement. The primary load path 1 thusincludes a rotary hollow screw 2 terminating at one of its ends in anattachment member, called the high primary clip 4, through which it isconnected to a structure 5 of the aircraft. Generally, the primary loadpath 1 also includes a nut (not shown) that cooperates with the screw bybeing assembled thereto and which is connected to the surface to becontrolled. The screw 2 is controlled in rotation by a motor, whichallows the nut to be moved in translation, the latter being blocked inrotation for this purpose. Movement in translation of the nut thusenables control of the deflection that it is desired to impart to thevariable horizontal surface.

A safety rod 3 passes through the interior of the hollow screw 2. Thesafety rod is one of the elements of the secondary load path 10.Generally, said rod 3 is terminated by a spherical head 7 positionedwith some play within a spherical recess of an attachment member 8 ofthe secondary load path, called the secondary high clip. Said secondaryhigh clip 8 is in its turn connected to the aircraft by means of anaircraft attachment member 9 different from that used to support theprimary load path 1. The attachment of the secondary high clip is knownper se, and is accomplished in particular by systems employingattachment clevises and screws.

In “normal” operation, it is the primary load path 1 which carries theloads. In the event of failure of the primary load path 1, particularlyby breakage of one of the elements constituting the primary load path 1,such as the high primary clip 4 or the screw 2 for example, it is thesecondary load path 10 that takes over the load. This fault must bedetected, in order to inform the pilot and if appropriate to initiatemaintenance operations on the ground or possibly in flight.

The primary load path failure detection device 13 is able to detect suchfaults. The primary load path failure detection device 13 includes aposition sensor 15 connected to the screw 2 to measure informationrepresenting its position. The sensor 15 may be an angular positionsensor 15. The angular position sensor 15 is configured to measure theangular position of the screw 2 and/or its angular displacement. Thismay involve angular displacement and/or angular positioning, which canbe absolute or relative depending on the conventions selected.Therefore, when the sensor 15 and the screw 2 are connected, the sensor15 measures the angular position of the screw 2. The angular positionsensor 15 can for example be an active electrical (inductive) rotationaldisplacement measurement sensor of the RVDT (Rotary VariableDifferential Transformer) type. Other angular position sensors can beused.

Alternatively, the information representing the position of the screwmay involve a linear position sensor, such as a linear displacementmeasurement sensor of the LVDT (Linear Variable DifferentialTransformer) type. In that case, the linear position sensor 15 isconnected to the screw 2 via a ballscrew type mechanism for example,which transforms the rotary motion of the screw 2 into a translatorymotion. The linear position sensor 15 therefore measures a position ordisplacement that is linear, but represents the angular position of thescrew 2.

Any position sensor 15 capable of measuring information representing theposition of the screw 2 can be used, that is to say that the informationmeasured (a position for example) is correlated to the angular positionof the screw 2 and thus allows the position of the screw to be deduced.

The primary load path failure detection device 13 includes adisconnection system 17 capable of disconnecting the screw 2 from theposition sensor 15 in the event of a relative displacement of the rod 3with respect to the screw 2 upon a break of the primary load path 1.Said disconnection therefore brings about the breakage of the connectionbetween the sensor 15 and the screw 2. Advantageously, the disconnectionsystem 17 is calibrated to disconnect the connection between the screw 2and the sensor 15 only in the event of a break of the primary load path1.

In the event of breakage of an element of the primary load path 1, it isthe secondary load path 10 which takes over the load. The rod 3 thenundergoes a relative displacement with respect to the screw 2, saiddisplacement being substantially oriented parallel to the screw 2, in atranslator motion in one direction or in the other. With this type ofsystem, the relative displacement of the rod 3 with respect to the screw2 is detected by the disconnection system 17, which then brings about adisconnection between the screw 2 and the position sensor 15. Saiddisconnection is triggered at the time that the relative displacement ofthe rod 3 with respect to the screw 2 or the magnitude of the loadapplied to the rod 3 exceeds a predetermined threshold for displacementor load, this threshold corresponding to a break of the primary loadpath 1. The threshold may, for example, be found from a simulation orfrom an in situ measurement. The aim is to avoid spurious detections dueto relative motion between the screw 2 and the rod 3 and/or loads on therod 3 that are not the result of a failure of the primary load path 1.Only a large enough load or a relative displacement of the rod 3 withrespect to the screw 2 above the threshold corresponds to a failure ofthe primary load path 1.

Below the predetermined threshold, the disconnection system 17 does notcut the connection between the screw 2 and the position sensor 15, whichavoids spurious detections. The disconnection system may include asensor or sensor suite measuring the relative movement of the rod 3 withrespect to the screw 2 (or conversely), which makes it possible todisconnect the screw 2 from the position sensor 15 only in the event ofa break of the primary load path 1. Alternatively, the disconnectionsystem 17 is configured to disconnect the position sensor 15 from thescrew 2 when the rod 3 exerts a predetermined load on the screw 2,corresponding to a mechanical force exerted by the rod 3 on the screw 2upon a break of the primary load path 1. Thus, a threshold for detectingfailure of the primary load path may be implemented with a solelymechanical system, avoiding the need for additional electricalcomponents. In the event of a break of the primary load path, the rod 3moves relative to the screw 2 and thereupon exerts a mechanical load onthe screw 2 that is greater than a predetermined threshold, saidmechanical load being used by the disconnection system 17 tomechanically disconnect the screw 2 from the position sensor 15 in theevent of a break in the primary load path 1.

The primary load path failure detection device 13 additionally includesa calculator 18 configured to compare the information representing theangular position of the screw 2 measured by the position sensor 15 andinformation representing the angular position of the screw 2 measured bya second position sensor 19 of the detection device 13. When theposition sensor 15 is disconnected then information from the two sensorswill not in agreement. It is therefore straightforward to determine whena failure of the primary load path is indicated by the primary load pathfailure detection device 13.

The information representing the angular position of the screw 2measured by the second position sensor 19 can be the angular positionitself or it may be a measurement of a linear position as mentionedabove. The second position sensor 19 differs from the sensor 15 in thatit is not connected to the screw 2 via the disconnection system 17. Thesecond position sensor 19 is therefore independent of the disconnectionsystem 17. Besides this difference, it is typically a sensor of the sametype, capable of measuring information representing the angular positionof the screw 2. If the two sensors are identical then it is simple tocompare their outputs to identify a primary load path failure.

This second position sensor 19 can be an angular position sensorbelonging to the aircraft itself, used to control and slave the rotationof the screw 2 in “normal” operation. It can advantageously be inparticular an angular position sensor connected with the screw 2 andexisting in all flight control actuators, which avoids installing newsensors. Advantageously, the position sensor 15 and the second positionsensor 19 are incorporated into one and the same multichannel sensor.

The primary load path failure detection device 13 therefore allows theuse of sensors already present on the aircraft, by simply integratingthe detection device 13, and particularly the disconnection system 17,into the actuator.

FIG. 3 shows a break of the primary load path 1 and a load takeover bythe secondary load path 10. The breakage is illustrated at the locationof the primary high clip 4, but may occur on any element participatingin the primary load path 1 of the actuator. Prior to said breakage, thatis to say during “normal” operation, the sensor 15 is connected to thescrew 2 and therefore measures information representing the angularposition of the screw 2. Furthermore, the screw 2 is controlled inrotation by the pilot via the flight commands that he communicates tothe aircraft. Information representing the angular position of the screw2 is measured by a second position sensor 19 which for its partcontinues to measure information representing the angular position ofthe screw 2 even in the event of a break in the primary load path 1,because it is not connected to the screw 2 via the disconnection system17.

In the event of a break in the primary load path 1, it is the secondaryload path 10 that bears the load. In this case, the rod 3 undergoes arelative displacement with respect to the screw 2, said displacementexceeding a predetermined threshold characteristic of a break of theprimary load path 1.

When this displacement exceeding the threshold occurs, the disconnectionsystem 17 brings about cutting of the connection between the screw 2 andthe position sensor 15. Consequently, the sensor 15 no longer measuresinformation representing the angular position of the screw 2. Theposition sensor 15 then measures a signal that is zero or constant,which allows detection of the break of the primary load path 1 and henceof the fault. The second sensor 19 continues to measure informationrepresenting the angular position of the screw 2 and the variations insaid positioning.

If the calculator 18 compares the signal from the second sensor 19 withthe signal measured by the position sensor 15 that has been disconnectedfrom the screw 2 by the disconnection system 17, it is clear that thesignals will be different, while prior to the fault these were equal orat least correlated. The calculator 18 is configured to detect a faultwhen the comparison between the information measured by the positionsensor 15 and the information measured by the second position sensor 19is greater or less than a predetermined threshold.

FIG. 4 shows a primary load path failure detection device 13 in moredetail. In this device 13 the disconnection system 17 includes abreakable pin 23, also known as a fuse pin. Said breakable pin 23 has across-section calibrated so as to break at a predetermined load,corresponding to a mechanical load exerted by the rod 3 on the screw 2upon a break in the primary load path 1 (breakage of the screw or ofanother element of the primary load path 1). This allows thedisconnection system 17 to operate automatically upon failure of theprimary load path 1 with only mechanical components and no furthersensors or the like. The pin 23 can be placed in a slot running throughthe screw 2 and the rod 3, or be screwed into a recess grooved for thispurpose. In addition, the axis of said breakable pin 23 is subjected toa predetermined extraction load, allowing extraction of the pin 23 fromthe screw 2 in the event of breakage of said pin 23. Said extractionload is exerted by pins 20, at right angles to the screw 2. Thebreakable pin 23 may connect the screw 2 to a pinion 22 which, via agear train, drives the position sensor 15, for example an angularposition sensor driven in rotation.

In the event of a break in the primary load path 1, and as illustratedin FIG. 5 the rod 3 exerts a mechanical load above the breakagethreshold of the pin 23, and this causes the pin 23 to break. Due to thespring load exerted on the pin 23, it disengages from the screw 3. Indisengaging, the pinion 22 becomes free to rotate, thanks in particularto a bearing 21. The pinion 22 therefore no longer follows the rotationof the screw 2, which means that the sensor 15 no longer measuresinformation representing the angular position of the screw 2, and isdisconnected from said screw 2, which allows detection of a break in theprimary load path 1.

When the calculator 8 compares the signal measured by the positionsensor 15 with the signal measured by the second position sensor 19, itdetects a fault when the comparison is greater (or less, as the case maybe) than a predetermined threshold.

It is desirable to be able to test the primary load path failuredetection device 13 in order to ensure that it is working correctly.Clearly, the disconnection device 17 could be tested by loading thesecondary load path, but this is undesirable as it would involvesignificant intervention on the aircraft, potentially through uncouplingthe primary load path, and it could also involve irreversible changes tosome components, for example the breakable pin 23. Thus, an additionalmechanism for checking the detection device would provide advantages,especially if it were possible to check the detection device without theneed to uncouple the primary load path or to damage breakable elementsof the primary load path failure detection device 13.

FIGS. 6 and 7 show an example arrangement for a primary load pathfailure detection device 13 adapted to include a check device. In thisexample, operation of the primary load path failure detection device 13is similar to that described above for FIGS. 4 and 5. The screw 2, whichpasses vertically through the centre of the elements shown in FIG. 6, iscoupled to mechanical parts in the form of feedback gears 32, 34, whichare themselves coupled to suitable position sensors, for example RVDTsensors. In normal use both of the two feedback gears 32, 34 rotate withthe screw 2, and hence they both provide the same indication of theposition of the screw 2. The first feedback gear 32 can be connected tothe position sensor 15 of the failure detection device 13, and thesecond feedback gear 34 can be connected to the second position sensor19 of the failure detection device 13. As described above, when theprimary load path fails then the failure detection device 13 willdisconnect the position sensor 15 so that there are different readingsprovided by this sensor and the second position sensor 19. In thisexample this is achieved via two breakable pins 23, which are mountedsymmetrically about the screw 2 and are described in more detail below.

The check device is implemented in such a way that when actuated itbrings about a temporary disconnection or uncoupling between theposition sensor 15 and the screw 2, thereby simulating a failure of theprimary load path. In this example the temporary uncoupling is achievedthrough a mechanical system that permits relative movement of the firstand second feedback gears 32, 34 compared to the screw 2, and relativemovement of the first feedback gear 32 compared to the second feedbackgear 34. This results in differing readings from the position sensor 15and the second position sensor 19, which means that the failure of theprimary load path is immediately evident and easily detected.

Considering the example arrangement of the breakable pin 23 in moredetail, with particular reference to FIG. 7, as seen in thecross-section the breakable pin 23 in this example has a neck part 36located across a join between a rod 3 of the secondary load path of theactuator and a screw 2 on the primary load path. As discussed above,when the primary load path fails then there will be an axial load on therod 3, which urges the rod 3 to displace axially relative to the screw2. The axial load, when beyond a certain threshold, will break thebreakable pin 23 at the neck 36. The neck 36 is carefully calibrated sothat it breaks at a suitable threshold indicative of failure of theprimary load path, and so that it does not break during normal use whenthere is no significant loading through the secondary load path and theprimary load path carries the load on the actuator.

There are two breakable pins 23 on opposite sides of the screw 2 asshown in FIG. 6. One pin 23 is connected to the first feedback gear 32,and the other pin 23 is connected to the second feedback gear 34. Thepins 23 form a part of the coupling between the feedback gears 32, 34and the screw 2, and enable linked movement of the feedback gears 32, 34and the screw 2 during normal use when the primary load path is intact.

FIG. 7 also shows the connections between the two feedback gears 32, 34and the screw 2 as well as the connections between one of the breakablepins 23 and the first feedback gear 32. During normal use, when thebreakable pins 23 are intact then both of the two feedback gears 32, 34will rotate to the same angular position dependent on the position ofthe screw 2. However, when the breakable pins 23 have sheared then thetwo feedback gears 32, 34 will no longer rotate together. Instead,gearing 38 in conjunction with bearings attaching the feedback gears 32,34 to the shaft have the effect that the second feedback gear 34 and thefirst feedback gear 32 will no longer rotate with the screw 2 and aredecoupled from each other. Thus, the sensors 15, 19 attached to thefeedback gears 32, 34 can be used to provide an indication of failure ofthe primary load path in the manner described above, for example using acalculator 18, since the two gears 32, 34 will appear to show differentpositions for the screw 2.

A small connecting rod 40 is coupled between the breakable pin 23 andthe first feedback gear 32 in such a way as to restrict relativerotational movement. The connecting rod 40 is located in a bore 42 onthe one side and a diagonal slot 44 on the other side. The diagonal slot44 is diagonal in the sense that it extends both radially andcircumferentially relative to the gear 32. In the example shown in thedrawings the bore 42 is coupled to the pin 23 and the slot 44 is formedon the gear 32, although it will of course be appreciated that theopposite arrangement could be used. FIG. 8 shows the diagonal slot inperspective view. It will be appreciated that a radial movement of theconnecting rod 40 relative to the gear 32 will result in a rotationalmovement of the gear 32. During normal operation the connecting rod 40does not move radially and so the feedback gears 32, 34 move together.When it is required to test the operation of the primary load pathfailure detection device 13 then the connecting rod 40 is moved radiallyin order to shift the first feedback gear 32 relative to the secondfeedback gear 42. As a result, a discrepancy is introduced between themeasurements from the position sensor 15 and the second position sensor19. This means that both mechanical and electrical aspects of theprimary load path failure detection device 13 can be tested, sinceduring radial displacement of the connecting rod 40 and the consequentrotational movement of the first feedback gear 32 then a failure of theprimary load path is simulated.

In this example radial movement of the connecting rod 40 is achieved byradial movement of the breakable pin 23 prompted by a force in thedirection shown in FIG. 7 by the arrow A. This force pushes thebreakable pin 23 inwards compressing a spring 46 and also moving theconnecting rod 40 radially inwards, thereby turning the first feedbackgear 32. It will be seen that the connecting pin 40 is held in a bore 42on a collar 48 attached to the breakable pin and movable therewith asthe spring 46 compresses. When the force in the direction A is removedthen the spring causes the assembly to move back to its normal position,returning the connecting rod 42 its usable position and rotating thefirst feedback gear 32 back into alignment with the second feedback gear34.

Thus, it will be understood that through this simple arrangement, andwithout the need for any additional sensors or complex components, itbecomes straightforward to simply test the mechanical and electricalcomponents of the primary load path failure detection device 13 byallowing for a temporary uncoupling simulating breakage of the primaryload path.

A further example arrangement for a check device is shown in FIG. 9, andthis Figure also shows the device in situ within a casing 49, with thecasing 49 being provided with an external actuator 50 that allows thecheck device to be actuated from outside of the casing 48. It will beseen that the check device of FIG. 9 also includes an additional featureto that of FIGS. 6 and 7, since as well as a spring 46 for compressionwhen the breakable pin 23 is pushed inwards, the device of FIG. 9 alsohas the collar 48 attached to the breakable pin 23 in a manner thatallows for relative radial movement, with a further spring 52 beingcompressed when the collar 48 is pushed inward relative to the breakablepin 23. This mechanism allows for a greater radial movement of theconnecting rod 40, as the collar 48 can move beyond the extent of therange of movement of the breakable pin 23. It will however beappreciated that the arrangement of FIG. 7 could replace the arrangementof FIG. 9 and be used in a similar casing 49 with a similar externalactuator 50.

Considering the external actuator 50 in more detail it will be seen thatthis takes the form of a spring-loaded pushbutton 54 that passes throughseals in the casing 49 in order to apply a force on the collar 48 and onthe breakable pin 23. In the example of FIG. 9 where the collar can moverelative to the breakable pin 23 then the pushbutton 54 has, at its end,a recess 56 to accommodate the relative movement. It will of course beappreciated that this recess 56 might not be necessary in the case thata slightly simpler arrangement of FIG. 7 was used.

FIG. 10 illustrates a testing apparatus for use in testing the checkdevice. The testing apparatus is arranged to simulate use of the checkdevice by actuating the mechanical linkage 40, 42, 44 of the checkdevice, which in turn is for simulating disconnection of the positionsensor 15 of the flight actuator primary load path failure detectiondevice 13 as discussed above. The testing apparatus includes a piston101 for contact with an actuator surface of the check device pin 23,which in this example is provided by the external actuator 50 of thecheck device. The external actuator 50 can be pushed against theresistance of its spring return to contact with the check device pin 23,which can then be pushed against the resistance of its return spring 52to test the primary load path failure detection device 13 as discussedabove. The piston 101 can hence be used to actuate the check deviceduring testing with the testing apparatus.

To use the testing apparatus it is first connected to the casing 49 ofthe check device via the addition of a suitable threaded lug (not shown)on the casing 49 and using a corresponding threaded section of amounting sleeve 102 of the testing apparatus. The mounting sleeve 102 iscoupled via a sleeve spring 103 to an inner sleeve 104 (piston guidepart) of the testing apparatus, with the sleeve spring 103 extendingbetween an internal shoulder of the mounting sleeve 102 and an externalshoulder of the inner sleeve 104. The external shoulder of the innersleeve 104 also contacts the internal surface of the mounting sleeve 102and the inner sleeve 104 is able to slide relative to the mountingsleeve 102, such that when the mounting sleeve 102 is mounted onto thecasing 49 then the inner sleeve 104 can slide relative to the casing 49.The piston 101 passes through the inner sleeve 104 and can slide withinthe inner sleeve 104 with a flange on the piston 101 in sliding contactwith the internal surface of the inner sleeve 104. A piston spring 105extends between the flange of the piston 101 and an internal shoulder ofthe inner sleeve. The piston 101 is prevented from sliding out of theinner sleeve 104 due to an O-ring at one end and the internal should ofthe inner sleeve 104 at the other end.

The piston spring 105 is softer than the spring return system for thecheck device pin so that when the testing apparatus is fitted to thecasing 49 then the piston 101 can be placed in contact with the endsurface (actuator surface) of the external actuator 50 without movementof the actuator 50, since the piston spring 105 will compress withoutsufficient force being generated to move the external actuator 50against the resistance from its spring and the spring 52 at the checkdevice pin 23.

When the testing apparatus has been mounted to the casing 49 via thescrew thread of the mounting sleeve 102 then it is adjusted to load thepiston spring 105 and to bring the internal shoulder of the inner sleeve104 into contact with a shoulder of the piston 101. This is done by theuse of an adjustment nut 106, which in this case is an outer sleeve thathas a threaded connection to the outside of the mounting sleeve 102. Theadjustment nut 106 holds a testing nut 107 that is fitted with athreaded connection to the adjustment nut 106. The testing nut 107 canbe brought into contact with the inner sleeve 104 to thereby apply aload to the piston spring 105 and slide the inner sleeve 104 against theresistance of the piston spring 105 to bring the internal shoulder ofthe inner sleeve 104 into contact with the shoulder of the piston 101.As explained above, whilst the load is carried by the piston spring 105then there is no movement of the check device since the piston spring105 is softer than the check device spring return.

When the adjustment nut 106 has moved sufficiently to bring the testingnut 107 into contact with the inner sleeve 104 and the inner sleeve 104is in contact with the piston 101 then an alignment marking 108 on theend of the piston 101 will become visible to the user. At this point thedistance between the adjustment nut 106 and the testing nut 107 providesa reference distance for checking operation of the check device. Thereference distance could be measured using any suitable measurementdevice, or it may in some cases be read from a scale provided on theadjustment nut 106 and the testing nut 107. To test the check device thetesting nut 107 is then tightened and bears against the inner sleeve104, which itself bears against the piston 101 to push the externalactuator 50 of the check device. The sleeve spring 103 compresses as thepiston 101 pushes the external actuator 50, and then as the testing nut107 is loosened the sleeve spring 103 returns the testing device to itsresting configuration. The load applied to the sensorless check devicevia the external actuator 50 and the maximum movement of the actuator 50can be limited by arranging the sleeve spring 103 so that it is fullycompressed and in coil to coil contact to stop further movement of thetesting nut 107 at a desired maximum movement of the external actuator50. Alternatively the movement of the testing nut 107 can be restrictedby suitable design of the testing nut 107, actuating nut 106 and/orinner sleeve 104 so that they come into contact at a desired maximummovement of the external actuator 50. The testing nut 107 is screwedinto the adjustment nut 106 for the full extent of its travel, which isset to correspond to an appropriate distance for actuation of the checkdevice. The testing nut 107 is then unscrewed until the alignmentmarking 108 is aligned with the end of the testing nut 107. Thisindicates that the piston 101 is being urged by the piston spring 105toward the external actuator 50 without movement of the actuator surface50, which in turn indicates that the external actuator 50, has reachedthe end of the movement urged by the spring return mechanism of thecheck device.

The relative distance between the adjustment nut 106 and the testing nut107 in the final position can then be measured again, and thismeasurement can be compared with the reference distance. If there is anydifference between the spacing of the adjustment nut 106 and the testingnut 107 before and after the test then this indicates that the checkdevice has not fully returned to its starting position, which means thatthe check device may not be operating correctly. On the other hand, ifthere is no difference (or a negligible difference) in the measurementsthen this indicates that the mechanical linkage 40, 42, 44 of the checkdevice is working correctly and that the check device has correctlydisengaged and re-engaged the first feedback gear 32.

1. A test apparatus for testing a sensorless check device of anactuator, wherein the sensorless check device is arranged to be used bymechanically moving a check device pin from a resting position to anactuation position and then releasing the check device pin to allow itto return to a resting position urged by an elastic return mechanism,the test apparatus comprising: a piston for contact with an actuatorsurface associated with the check device pin; a piston spring for urgingthe piston toward the actuator surface, wherein the piston spring issofter than the elastic return mechanism of the check device; and anadjustment and testing mechanism; wherein the adjustment and testingmechanism is arranged to: compress the piston spring and apply a loadvia the piston to the actuator surface to move the actuator surface sothat the position of the piston at the start of the movement of theactuator surface can be recorded in order to establish a referenceposition, depress the check device pin via the piston and actuatorsurface to simulate use of the check device, allow the check device pinto return toward the reference position being urged by its elasticreturn mechanism, and indicate when the check device pin reaches a finalposition after being released by indicating when the actuator surface isno longer applying a force to the piston, such that the final positionof the check device pin can be compared to the reference position.
 2. Atesting apparatus as claimed in claim 1, including a mounting part forattachment of the testing apparatus to a casing that surrounds the checkdevice via a coupling mechanism for securely anchoring the testingapparatus to the casing.
 3. A testing apparatus as claimed in claim 1,wherein the adjustment and testing mechanism includes: an adjustmentpart arranged for movement relative to other parts of the testingapparatus in order to compress the piston spring and bear against thepiston to allow a load to be applied to the actuator surface via thepiston; and a testing part arranged for movement relative to other partsof the testing apparatus in order to move the piston and to apply a loadto the actuator surface via the piston in order to move the check devicepin against the resistance of the elastic return mechanism.
 4. A testingapparatus as claimed in claim 3, wherein the reference position and thefinal position are determined by aligning the testing part of theadjustment and testing mechanism with an alignment marking on the pistonand then measuring a distance between the testing part and theadjustment part of the adjustment and testing mechanism.
 5. A testingapparatus as claimed in claim 3, wherein the adjustment part of theadjustment and testing mechanism is moveably attached to the mountingpart and the testing part of the adjustment and testing mechanism ismoveably attached to the adjustment part.
 6. A testing apparatus asclaimed in claim 5, wherein the moveable attachments include screwthreads.
 7. A testing apparatus as claimed in claim 6, wherein thetesting nut is configured to be screwed and unscrewed in order todepress the check device pin via the piston and actuator surface and tothen allow the check device pin to return under toward its startposition the influence of the elastic return mechanism.
 8. A testingapparatus as claimed in claim 1, comprising a piston guide part forholding the piston, guiding motion of the piston, and holding the pistonspring such that the piston spring can be compressed between the pistonand the piston guide part.
 9. A testing apparatus as claimed in claim 8,wherein the piston guide part takes the form of an inner sleeve that islocated about the piston and fits closely with the piston in order toguide a sliding motion of the piston within the inner sleeve, whereinthe piston guide part includes a shoulder for engaging with and pushingthe piston, and wherein the adjustment and testing mechanism is arrangedto come into contact with the piston guide part in order to push theshoulder of the piston guide part into engagement with the piston inorder to move the piston and thereby move the check device pin.
 10. Atesting apparatus as claimed in claim 9, wherein the adjustment andtesting mechanism includes an adjustment part and a testing part, andwherein the testing part is brought into contact with the piston guidepart in order to push the shoulder of the piston guide part intoengagement with the piston by movement of the adjustment part to movethe testing part relative to the mounting part.
 11. A testing apparatusas claimed in claim 1, wherein the testing apparatus includes: amounting part in the form of a mounting sleeve with a coupling mechanismfor securely anchoring the testing apparatus to the casing; an innersleeve that is held for sliding movement relative to the mountingsleeve, wherein the inner sleeve holds and guides motion of the piston,holds the piston spring such that the piston spring can be compressedbetween the piston and the inner sleeve, and includes a shoulder forengaging with and pushing the piston; an adjustment part in the form ofan adjustment nut moveably attached to the mounting sleeve; and atesting part in the form of a testing nut moveably attached to theadjustment nut; wherein movement of the adjustment nut will bring thetesting nut into contact with the inner sleeve to load the piston springand bring the shoulder of the inner sleeve into engagement with thepiston; wherein subsequent movement of the testing nut will move thepiston to thereby move the actuator surface in order to allow for thecheck device pin to be depressed; and wherein the piston is providedwith an alignment marking for alignment with the testing nut in order todetermine the reference position and the final position.
 12. A systemfor checking a flight actuator, wherein the flight actuator comprises asensorless check device, wherein the system comprises the sensorlesscheck device and a testing apparatus as claimed in claim 1, and whereinthe sensorless check device is a check device for a flight actuatorprimary load path failure detection device of the type that disconnectsa position sensor from the primary load path in the event of a primaryload path failure, the check device comprising: a mechanical linkage forsimulating disconnection of the position sensor by permitting relativemovement of at least first and second mechanical parts of the actuatorthat are unable to move relative to one another in normal use withoutfailure of the primary load path, wherein these first and secondmechanical parts include a first mechanical part with movement detectedby the position sensor of the primary load path failure detectiondevice.
 13. A system as claimed in claim 12, wherein the mechanicalparts are gears coupled to a screw in a primary load path of theactuator, the gears being arranged such that in normal use they rotatetogether, and the mechanical linkage of the check device being arrangedsuch that, when actuated, it moves one of the gears relative to theother.
 14. A method for testing the operation of a sensorless checkdevice for a primary load path failure detection device, wherein thesensorless check device has an actuator surface associated with a checkdevice pin and an elastic return mechanism for returning the actuatorsurface and the check device pin to a start position after use, themethod comprising: bringing a piston of a testing apparatus into contactwith an actuator surface associated with the check device pin, wherein apiston spring of the testing apparatus urges the piston toward theactuator surface, and wherein the piston spring is softer than theelastic return mechanism of the check device; compressing the pistonspring until a load can be applied via the piston to the actuatorsurface to move the actuator surface; recording the position of thepiston at the start of the movement of the actuator surface in order toestablish a reference position; depressing the check device pin usingthe testing apparatus to simulate use of the check device; releasing thecheck device pin and allowing it to return toward the reference positionbeing urged by its elastic return mechanism; determining when the checkdevice pin reaches a final position by determining when the actuatorsurface is no longer applying a force to the piston; and comparing thefinal position of the check device pin to the reference position toensure that the check device pin returns to its original position.